1. Field of the Invention
The present invention relates to a wireless communication system, weak radio wave communication device, mobile terminal device, base station device, and program which process data by transmitting the data from the weak radio wave communication device, for example, one of wireless tags disposed in a dispersed manner in a wireless LAN environment in which access points are installed, to the mobile terminal device such as a portable phone, and particularly relates to the wireless communication system, weak radio wave communication device, mobile terminal device, base station device, and program for reliably transmitting data to the mobile terminal device even by weak radio waves from the wireless tag.
2. Description of the Related Arts
Recently, there has been conceived a system in which wireless tags known as communication devices that transmit/receive data by weak radio waves are disposed at various locations, and, for example, position information is received from the wireless tags by a mobile terminal such as a portable phone so as to recognize that it is in the vicinity of the wireless tag. A communication module adapted for an IEEE 802.11 wireless local area network (hereinafter, referred to as “wireless LAN”) is used as a communication module of such a wireless tag, a utilization environment in which access points serving as base stations of a wireless LAN, for example, a wireless LAN environment of, for example, a facility or a shop is built, and wireless tags are disposed therein in a dispersed manner so that position information or commercial product information can be transmitted to and utilized by a portable terminal which is carried by a user and on which a communication module adapted for the wireless LAN is mounted.
However, when the wireless tags that emit merely weak radio waves are disposed in a dispersed manner in a wireless LAN environment, the mobile terminal communicates with the access points, in addition to communication with the wireless tags, by strong radio waves by using a frequency band same as that of the wireless tags; therefore, there is a problem that the weak radio waves of the wireless tags are interrupted by the strong radio waves between the mobile terminal and the access points, and the signals from the wireless tags cannot be readily received. In such a case in which radio waves from a plurality of devices collide with each other, generally, mutual interference is avoided by a collision avoiding technique such as CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance). CSMA/CA is a method in which the state of the surrounding area is monitored before emitting radio waves, transmission operation is started merely when no one is performing transmission, and, when someone is performing transmission, termination of the communication is waited for to try transmission again. However, in order to cause CSMA/CA to be effective, the radio waves of the wireless tags are required to reach all the access points and other mobile terminals, and there is a problem that it does not effectively function by the wireless tags that emit merely weak radio waves.